These functions perform miscellaneous control actions on terminal
devices. As regards terminal access, they are treated like doing
output: if any of these functions is used by a background process on its
controlling terminal, normally all processes in the process group are
sent a SIGTTOU
signal. The exception is if the calling process
itself is ignoring or blocking SIGTTOU
signals, in which case the
operation is performed and no signal is sent. See section Job Control.
This function does nothing if the terminal is not an asynchronous serial data port.
The return value is normally zero. In the event of an error, a value
of @math{-1} is returned. The following errno
error conditions
are defined for this function:
EBADF
ENOTTY
tcdrain
function waits until all queued
output to the terminal filedes has been transmitted.
This function is a cancelation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time tcdrain
is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to tcdrain
should be
protected using cancelation handlers.
The return value is normally zero. In the event of an error, a value
of @math{-1} is returned. The following errno
error conditions
are defined for this function:
EBADF
ENOTTY
EINTR
tcflush
function is used to clear the input and/or output
queues associated with the terminal file filedes. The queue
argument specifies which queue(s) to clear, and can be one of the
following values:
TCIFLUSH
TCOFLUSH
TCIOFLUSH
The return value is normally zero. In the event of an error, a value
of @math{-1} is returned. The following errno
error conditions
are defined for this function:
EBADF
ENOTTY
EINVAL
It is unfortunate that this function is named tcflush
, because
the term "flush" is normally used for quite another operation--waiting
until all output is transmitted--and using it for discarding input or
output would be confusing. Unfortunately, the name tcflush
comes
from POSIX and we cannot change it.
tcflow
function is used to perform operations relating to
XON/XOFF flow control on the terminal file specified by filedes.
The action argument specifies what operation to perform, and can be one of the following values:
TCOOFF
TCOON
TCIOFF
TCION
For more information about the STOP and START characters, see section Special Characters.
The return value is normally zero. In the event of an error, a value
of @math{-1} is returned. The following errno
error conditions
are defined for this function:
EBADF
ENOTTY
EINVAL
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